1. Field of the Invention
The present invention relates to an aqueous dispersion of a block copolymer. The aqueous dispersion of the invention has good adhesiveness, especially airtight adhesiveness, to various substrates, and has good stability. In addition, the aqueous dispersion of the invention gives a coating layer of good properties in water resistance, weather resistance, gloss and resistance to solvent attack.
2. Discussion of the Background
Polyolefins such as polypropylene have good properties including processability, water resistance and oil resistance, and are inexpensive. Therefore, they are widely used for plastics for electric and electronic appliances for household use and for automobile parts. In some cases, polyolefins are made into moldings coated with paint or made into laminates with other resins. However, due to their low polarity, polyolefins have a problem that they are poorly adhesive to ordinary paint and to other resins.
To solve the problem, it has been tried that the surface of polyolefin moldings are treated with chromic acid, flame, corona discharge, plasma, solvent, etc. to increase the polarity of the surface of the moldings and to improve the adhesiveness thereof to paint and other resins. However, the treatment requires complicated working steps and requires a large amount of corrosive chemicals, and is therefore often dangerous.
Under such situation, a method of applying a primer that comprises, as the essential ingredient, a chlorinated polyolefin to the surface of polyolefin moldings has been proposed. However, the chlorinated polyolefin is usually used as a solution in an aromatic organic solvent, such as toluene and xylene, which is harmful to human. Therefore, the use of a primer comprising chlorinated polyolefin is undesirable in view of environmental safety. A method of dispersing such a chlorinated polyolefin in water has been proposed (see Japanese Patent Laid-open Nos. 256556/1989 and 218548/1992). Even in this method, however, it is still difficult to prepare the aqueous dispersion without using such an aromatic organic solvent at all. In addition, the weather resistance and water resistance of the coating layer formed by the aqueous dispersion is poor.
Furthermore, aqueous dispersion type adhesive compositions free of a chlorinated substance are desired from the viewpoint of recycling or suppression of a hydrogen chloride gas generation upon waste incineration, etc.
One object of the present invention is to provide an aqueous dispersion which has good adhesiveness, especially airtight adhesiveness to various substrates, good stability, and results in a coating layer having excellent water resistance, weather resistance and the like.
The present invention provides an aqueous dispersion which includes i) an aqueous dispersion (I) of a block copolymer (I) comprising at least one polymer block (A) containing olefin monomer units and at least one polymer block (B) containing 2 to 100 mole percent of units derived from at least one vinyl monomer having a carboxyl or carboxylic anhydride group and 98 to 0 (zero) mole percent of units derived from another vinyl monomer or monomers copolymerizable with the carboxyl group- or carboxylic anhydride group-containing vinyl monomer, in an aqueous solution of not less than 0.05 equivalent, relative to the carboxyl or carboxylic anhydride group, of a basic substance, and ii) a polyurethane (II) incorporated in the aqueous dispersion (I).
The invention also provides an aqueous dispersion which includes i) an aqueous dispersion (I) of a block copolymer (I) comprising at least one polymer block (A) containing olefin monomer units and at least one polymer block (B) containing 2 to 100 mole percent of units derived from at least one vinyl monomer having a carboxyl or carboxylic anhydride group and 98 to 0 (zero) mole percent of units derived from another vinyl monomer or monomers copolymerizable with the carboxyl group- or carboxylic anhydride group-containing vinyl monomer, in an aqueous solution of not less than 0.05 equivalent, relative to the carboxyl or carboxylic anhydride group, of a basic substance, and iii) an aqueous dispersion or an aqueous solution (III) of a vinyl polymer (III) incorporated in the aqueous dispersion (I).
The invention further provides an aqueous dispersion which includes i) an aqueous dispersion (I) of a block copolymer (I) comprising at least one polymer block (A) containing olefin monomer units and at least one polymer block (B) containing 2 to 100 mole percent of units derived from at least one vinyl monomer having a carboxyl or carboxylic anhydride group and 98 to 0 (zero) mole percent of units derived from another vinyl monomer or monomers copolymerizable with the carboxyl group- or carboxylic anhydride group-containing containing vinyl monomer, in an aqueous solution of not less than 0.05 equivalent, relative to the carboxyl or carboxylic anhydride group, of a basic substance, and iv) a tackifier (IV) incorporated in the aqueous dispersion (I).